The invention relates to random access memory for data storage. More specifically, the invention relates to a magnetic random access memory device including an array of memory cells.
Magnetic Random Access Memory ("MRAM") is a non-volatile memory that is being considered for long term data storage. Performing read and write operations on MRAM devices would be orders of magnitude faster than performing read and write operations on conventional long term storage devices such as hard drives. In addition, the MRAM devices would be more compact and would consume less power than hard drives and other conventional long term storage devices.
A typical MRAM device includes an array of memory cells. Word lines extend along rows of the memory cells, and bit lines extend along columns of the memory cells. Each memory cell is located at a cross point of a word line and a bit line. A memory cell stores a bit of information as an orientation of a magnetization. The magnetization orientation of each memory cell assumes one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of "1" and "0." The magnetization orientation of a selected memory cell may be changed by supplying currents to a word line and a bit line crossing the selected memory cell. The currents create two orthogonal magnetic fields that, when combined, switch the magnetization orientation of a selected memory cell from parallel to anti-parallel or vice versa.
However, switching of the memory cells is not always reliable. Sometimes, the combined magnetic fields might not cause a memory cell to switch reliably from parallel to anti-parallel, or vice-versa. This problem is typically solved by increasing crystal anisotropy, coercivity or aspect ratio of the memory cells.
However, increasing the crystal anisotropy, coercivity or aspect ratio leads to another problem: the amount of current for switching the memory cells is also increased. Increasing the amount of current increases the amount of power consumed by the MRAM device. Increasing the amount of current also results in larger bit and word lines and write circuits to handle the higher currents. Resulting is a larger, more expensive MRAM device.
Therefore, a need exists to improve reproducibility or reliability of switching MRAM devices without increasing the switching current.